Field of the Invention
The present disclosure relates to a thin film transistor (or “TFT”) substrate having a high reliability oxide semiconductor material including a metal oxide semiconductor material. Especially, the present disclosure relates to a TFT substrate having a metal oxide semiconductor material such as Indium-Gallium-Zinc oxide material doped with the gaseous impurity elements such as nitrogen.
Discussion of the Related Art
Nowadays, as a lot of portable appliances such as the mobile phone, the personal digital assistant, and the notebook computer are fluently used, and various flat panel display devices are developed for overcoming many drawbacks of the cathode ray tube such as heavy weight and bulk volume. The flat panel display devices include the liquid crystal display device (or LCD), the field emission display (or FED), the plasma display panel (or PDP), and the organic light emitting diode display (or OLED). Because of compatibility with mass production technology, easiness of driving means, high quality & high resolution display, and/or low power consumption, the flat panel displays, including the liquid crystal displays and/or the organic light emitting diode displays, adopt a substrate having a plurality of thin film transistors arrayed in a matrix manner, so it is called the ‘active matrix type thin film transistor substrate’.
The most used active matrix type thin film transistor substrates use the amorphous silicon thin film transistor as the switching element for driving the pixels. As the amorphous silicon thin film transistors have some merits of low manufacturing price and the relatively lower temperature process than other thin film transistors, they are widely adopted for the switching elements of the thin film transistor substrates for the flat panel display.
However, as the amorphous silicon material has the lower mobility and the inferior electrostatic property (or “constant current property”) than others, the large area display using them as the switching elements may be hard to ensure good quality. To overcome these disadvantages of the amorphous silicon elements, the thin film transistor having poly-silicon materials are applied to the flat panel display. The thin film transistor including the poly-silicon materials also has disadvantages such as high manufacturing cost difficulty in ensuring uniform properties of the semiconductor material over the whole surface of the substrate and a very high temperature manufacturing process. Further, the electrostatic property of the poly-silicon material is not better than that of the amorphous silicon material but is rather at a similar level.
To overcome these problems, recently, the oxide thin film transistor including oxide semiconductor material is suggested for application to flat panel displays. As the oxide thin film transistor can be manufactured in lower temperature processes and its electrostatic property is much superior to the amorphous silicon material and the poly-silicon material, it is possible to obtain a thin film transistor for the flat panel display having better property and characteristics with lower price.
For the currently focused material in the oxide semiconductor, there are some materials based on Zinc Oxide such as the Indium-Zinc Oxide (or “IZO”), Indium-Gallium-Zinc Oxide (or “InGaZnO”), and/or Indium-Tin-Zinc Oxide (or “ITZO”). Especially, amorphous Indium-Gallium-Zinc Oxide (or “a-InGaZnO4: a-IGZO”) is one of the best materials. As a-IGZO thin film transistor substrate can be manufactured using the same processes and equipments used for amorphous silicon thin film transistor substrate with better quality, it is not required to invest for manufacturing and/or fabricating equipments. That is, the conventionally used equipments can be used as is. As for the depositing method for a-IGZO, the sputtering method is the best for commercializing, among various methods.
For the thin film transistor having the oxide semiconductor material, the top gate structure and the bottom gate structure can be applied. When the bottom gate structure is applied to the oxide thin film transistor, the back channel etched type and the etch stopper type can be considered. Especially, the etch stopper type is better for getting high quality.
Even though the IGZO semiconductor materials have many merits, they also have some disadvantages. For example, the property and/or the reliability of the oxide semiconductor thin film transistor may be degraded, when it is used for a long time. It is noticed that this degradation is caused by defects in the layers of the oxide semiconductor material.
In order to ensure the reliability of the thin film transistor including the metal oxide semiconductor materials, there are some conventional methods. For example, the oxide semiconductor material is isolated from the outer material or a plasma treatment is conducted to the oxide semiconductor material. However, these methods cannot be the fundamental solution. Further, these methods require any additional processes and/or the expensive equipments.
For example, a method is suggested in which the plasma treatment is conducted after the IGZO thin film is deposited. This method requires additional plasma treatment equipment so that additional manufacturing price is required and the manufacturing time is longer. Further, the IGZO film may be damaged by the plasma treatment process. The recovery process may be required after the plasma treatment which may increase the manufacturing time and cost.
For another method, by depositing the aluminum oxide (Al2O3) layer on the IGZO surface, the reliability of the IGZO can be enhanced. In that case, as the process for depositing the aluminum oxide layer is added after forming the IGZO semiconductor layer, the cost and the time for manufacturing the device is increased. Even though the aluminum oxide layer may protect the IGZO from external air causing the degradation of the reliability, the reliability by the defects from the IGZO thin film itself cannot be solved.
For still another method, there is a thermal treatment under high oxygen gas pressure. This is for enhancing the reliability by reducing the oxygen vacancy that is one of the reasons for the defects of the IGZO thin film itself. As this method requires specific oxygen thermal treatment equipment, the cost and time for this thermal treatment are required. Further, as the oxygen particles are implanted into the IGZO semiconductor material, the characteristics of the IGZO semiconductor material may be changed. In the case that the oxygen occupies the vacancy in the IGZO material, the electron mobility may be remarkably degraded.
Consequently, for manufacturing the thin film transistor and/or the thin film transistor substrate having oxide semiconductor material, a method for solving the defects due to the characteristics of the oxide semiconductor material is needed. Further, the method should enhance the reliability of the oxide semiconductor material without any additional cost and process steps for manufacturing a device having the oxide semiconductor material.